Organic EL devices have been intensively studied since Eastman Kodak Company found an organic EL device (see, for example, Non-patent Document 1) that shows a characteristic of about 1000 cd/m2 at a drive voltage of 10 V or below. Organic EL devices can be broadly classified into low molecular weight organic EL (hereinafter abbreviated as OLED) and EL using polymer light-emitting materials (hereinafter abbreviated as PLED). In either case, in order to improve initial characteristics such as a low drive voltage and a high emission efficiency and also ensure a prolonged life of the device, the usual practice is to use a hole injection layer or a hole transport layer.
However, CuPC that is an ordinary hole injection material in OLED (see, for example, Non-patent Document 2) is insoluble in a diversity of solvents, so that vacuum deposition is necessary for film formation. For this reason, the resulting film has a drawback in that the film are greatly irregular and that if other organic layer is incorporated with the material in a very small amount, characteristic properties greatly lower, coupled with another problem that this material cannot be used as a hole transport layer of PLED. In addition, it has been reported that CuPC has an absorption in a visible range and is thus low in transparency, influencing the color tone of light from the device.
On the other hand, polyaniline materials (see, for example, Non-patent Documents 3, 4) and polythiophene materials (see, for example, Non-patent Documents 5) used as a hole transport layer of PLED are low in solubility in organic solvents. Eventually, the thin film obtained from a varnish containing these materials is in conveniently brittle and small in mechanical strength, with its heat resistance being poor. When a solvent is removed, powder is liable to be formed, with the problem involved in the uniformity and flatness of the thin film. This powder formation promotes the occurrence, of dark spots and the lowering of device characteristics resulting from the short-circuiting between an anode and a cathode, and causes a yield to be lowered at the stage of producing an organic EL device.
Mixed materials of polyimides with polyaniline materials have been reported so as to improve the mechanical strength and heat resistance of a charge transporting thin film (see, for example, Patent Document 1). In this case, for enhancing charge transportability of the thin film, it is needed to increase a ratio of polyaniline in the mixture. However, if the content of the polyaniline is increased, powder is apt to be formed due to the low solubility thereof, with the attendant problem that a uniform and flat thin film cannot be obtained.
Hence, the problems on the mechanical strength, heat resistance, uniformity and flatness of the charge transporting thin film have never been solved yet satisfactorily.
For organic EL devices, there is a demand of developing such a device that has a high emission efficiency at low drive voltage and is good in economy. To this end, the charge transporting thin film should have, aside from excellent charge transportability, high transparency so as to improve the emission efficiency of the device.    Non-patent Document 1:    Applied Physics Letters, U.S.A. 1987, Vol. 51, pp. 913 to 915    Non-patent Document 2:    Applied Physics Letters, U.S.A. 1996, Vol. 69, pp. 2160 to 2162    Non-patent Document 3:    Nature, U.K. 1992, Vol. 357, pp. 477 to 479    Non-patent Document 4:    Applied Physics Letters, U.S.A. 1994, Vol. 64, pp. 1245 to 1247    Non-patent Document 5:    Applied Physics Letters, U.S.A. 1998, Vol. 72, pp. 2660 to 2662    Patent Document 1:    JP-A 11-185962